This invention is generally related to automatic data collection (xe2x80x9cADCxe2x80x9d) and more particularly to automatic data collection employing color machine-readable symbols selected from a color symbology.
Bar code scanners and wand-based readers (xe2x80x9creadersxe2x80x9d) scan and decode typical bar codes from linear symbologies. xe2x80x9cLinear symbologiesxe2x80x9d are symbologies where data is encoded as parallel arrangements of alternating, multiple-width bars and spaces (e.g., U.P.C., Code 39, Code 93, etc.). Linear symbologies, as well as other symbologies, encode xe2x80x9cdata charactersxe2x80x9d (i.e., human-readable characters) as xe2x80x9csymbol characters,xe2x80x9d which are typically alternating bars and spaces. In typical linear symbologies, such as Code 39, each bar and space, or xe2x80x9celement,xe2x80x9d in the symbol is one of four narrow and wide elements: a single-width bar, a single-width space, a double-width bar or a double-width space. More complex linear or stacked symbologies employ a greater number of widths for each element.
Bar code readers typically convert symbol characters to data characters by scanning an area to produce a reflectance signal or bar code xe2x80x9cprofile,xe2x80x9d which is generally an analog signal representing the modulated light reflected from areas of high reflectance or xe2x80x9cspaces,xe2x80x9d and absorbed by areas of low reflectance or xe2x80x9cbars.xe2x80x9d As a result, the profile represents the pattern of bars and spaces, or xe2x80x9celements,xe2x80x9d in the symbol. In a given profile, a peak corresponds to a space (high reflectivity), while a valley corresponds to a bar (low reflectivity, relative to the space). The width of each peak or valley generally indicates the width of the corresponding bar or space whose reflectance produced the peak or valley.
Many bar code readers employ xe2x80x9cwave shapingxe2x80x9d circuits that essentially square off the profile based on transitions or vertical edges between the peaks and valleys in the profile. Counting circuits then produce a series of counts that indicate the horizontal widths of the bars and spaces from the linear bar code symbol. A typical locating algorithm in the reader locates a bar code symbol by examining the series of counts to attempt to find a quiet zone and an adjacent start/stop symbol character. A xe2x80x9cquiet zonexe2x80x9d is a clear space, containing no dark marks, that precedes or follows a symbol, often next to a start or stop character. xe2x80x9cStart and stop charactersxe2x80x9d are symbol characters, unique to a given symbology, that indicate the beginning and end of a given symbol, respectively. Typically, a quiet zone has a size that is about ten times greater than bars that precede or follow the quiet zone. Therefore, the reader examines a series of counts and attempts to find a count that is approximately ten times greater than a count which follows thereafter. Once the quiet zone and adjacent start/stop character have been located, standard decode algorithms are employed to decode series of counts from the symbol into data characters.
Wand-type readers contact the surface on which the bar code is printed. Such readers often produce profiles having sharp contrast between the peaks and valleys and thus the spaces and bars represented by the profile are easily detectable by circuitry in the reader. However, wand-type readers require the wand to contact the surface on which the bar code is printed, and are thus impractical in situations where a user cannot or does not wish to physically contact the bar code. Requiring the user to manually contact each bar code is time consuming and reduces productivity.
Non-contact bar code readers are currently available such as laser scanning and linear charge-coupled device (xe2x80x9cCCDxe2x80x9d) readers. Laser scanning-type readers employ a scanning beam of laser light which impinges on and is reflected from a bar code. A photodetector receives the reflected light and converts it into a modulated electrical signal that comprises the profile for the bar code.
Wand-based readers and laser scanners are often adequate to scan and decode linear symbologies. However, newer data collection symbologies have departed from the typical linear symbologies to create stacked or area symbologies in order to increase xe2x80x9cinformation density,xe2x80x9d i.e., the amount of information encoded within a given area. xe2x80x9cStacked symbologies,xe2x80x9d or multi-row symbologies, employ several adjacent rows of multiple-width bars and spaces (e.g., Code 49, PDF417, etc.). xe2x80x9cArea symbologiesxe2x80x9d or two-dimensional matrix symbologies, employ arrangements of regular polygon-shaped data cells where the center-to-center distance of adjacent data cells is uniform (e.g., MaxiCode, Code One, Data Matrix, Aztec Code, etc.).
One symbology, similar to MaxiCode, described in U.S. Pat. No. 4,998,010, uses three colors of hexagonal data cells, white, black and grey. The use of color and/or shading can increase the information density of machine-readable symbols. Such non-black and white or xe2x80x9ccolorxe2x80x9d symbologies have yet to realize significant commercial success, at least partially due to technological problems associated with reading color symbols. Attempts to read color symbols have relied on two-dimensional image sensors, typically color sensors. Stacked and area symbologies also typically require image or vision-based readers that produce two-dimensional images of a field of view. Image or vision-based readers employ two-dimensional semiconductor arrays, vidicons, or other suitable light receiving elements that receive an image of a bar code and, based on the light reflected therefrom, process the image to produce a profile or other signals.
For color symbols, such devices read color in sequential steps, limiting such readers to fixed mount reading devices. See, e.g., U.S. Pat. No. 3,684,868. Fixed mount readers are not practical in a large variety of applications that require mobility, and thus place undue limitations on the use and commercial acceptance of color machine-readable symbologies. Other drawbacks of such devices can include the relatively high cost of two-dimensional video charge coupled devices and the relatively small depth-of-field of such devices as compared to laser scanning symbol readers.
Due to optical system limitations inherent in laser- or image-type readers, these readers have a specified depth-of-field within which bar codes can be read. If a reader scans or images a bar code out of its depth-of-field, the resulting profile will exhibit xe2x80x9cclosure.xe2x80x9d Positive ink spread in a bar code or excessive noise in a profile can also produce closure. Closure in a bar code profile is evidenced by some recognizable peaks and valleys, but also ripples in the middle of the profile. Closure in a bar code profile generally indicates that the wide elements in the profile are resolved, but that the narrow elements are unresolved. With respect to readers, a space or bar is xe2x80x9cresolvedxe2x80x9d if the reader is able to identify a peak or valley in the profile that corresponds to the given space or bar. Some profiles may represent narrow elements by small peaks, valleys or ripples that are visually recognizable, but which are essentially undetectable by current readers.
Typical readers are unable to decode profiles having closure. As noted above, these readers typically employ wave shaping circuits to find the edges of bar code elements represented in a profile. To decode each element in the bar code, these electronic circuits locate an edge of an element as a point where, for example, the reflectance in the profile reaches a fixed distance from a peak or valley. Currently available readers cannot decode profiles where the narrow elements are out-of-focus or lost in the profile (i.e., profile closure) because the narrow elements fail to produce any significant peaks or valleys and thus the wave shaping circuitry is unable to locate any edges in the profile corresponding to these elements. Since current wave shaping circuits cannot locate the narrow elements in a profile when closure occurs, the circuits cannot decode the bar code.
Recently, the inventor has discovered method and corresponding apparatus for decoding machine-readable symbols profiles exhibiting closure. U.S. Pat. Nos. 5,389,770, 5,486,689, 5,514,858, 5,539,191, 5,798,513 and 5,877,486 and U.S. patent application Nos. 09/133,387 and 09/185,905, entitled xe2x80x9cMethod and Apparatus for Decoding Unresolved Profiles Produced from Relief Formed Symbolsxe2x80x9d and xe2x80x9cMethod and Apparatus for Decoding Unresolved Symbol Profiles Produced from a Reduced Data Setxe2x80x9d respectively, explain such methods and apparatus in detail. Reading color symbols with a single color reader, such as a laser scanner with a red laser, will produce profiles similar to profiles that exhibit closure. Consequently, existing readers that read standard black and white symbols are unable to read and decode color symbols. As noted above, the only existing readers capable of reading color symbols are expensive. Furthermore, such readers are limited to fixed mount applications.
Under an aspect of the invention and for ease in explaining the concepts, a reader, such as a laser scanner, uses existing components in standard readers to decode color symbols. The reader is capable of scanning or reading simple color bar code symbols that have two-color wide elements, for example, red and blue wide elements. Elements of a third color, such as yellow, exhibit closure like behavior in a manner found to be similar to out-of-focus decoding. Such a symbology, for example, may be similar to the known Code 39 symbology, but where wide bars are, e.g., blue, wide spaces are red, and all narrow elements are yellow. When seen with a single color red laser scanner, red bars form peaks, blue bars form valleys, and yellow elements form intermediate reflectance values in the profile. By using the located centers of the red and blue elements in a profile, as well as the amplitude of the signal in the profile, a simple algorithm and processor decodes the profile by identifying the yellow elements in a similar fashion to profiles exhibiting closure.
The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.